It is well known to win mineral, e.g. coal, with the aid of a machine such as a plough which is hauled back and forth along a scraper-chain conveyor. The plough is propelled with the aid of a chain driven with drive means at a drive station at one end of the conveyor. In such an installation it necessary to adjust the tension in the drive chain from time to time. Normally the drive chain is entrained around a chain wheel in a housing, the so-called "plough box" which is moved along with associated drive motor and gearing in relation to a machine frame of the drive station to adjust the tension.
In DE-OS 2554785 a hydraulic piston and cylinder unit is used to move the plough box. The cylinder of the unit is mounted to a side plate of the frame and the plough box is fixed in a variety of pre-set positions by a locking member such as a bolt, engaging in a row of holes after the unit has adjusted the chain tension.
There is a need for an improved chain tensioning system.